A. Field of the Invention
The present invention relates to a method for manufacturing a silicon carbide semiconductor device.
B. Description of the Related Art
Compound semiconductors using four-layered hexagonal silicon carbide (4H—SiC) as a semiconductor material are known. When a power semiconductor device is manufactured using 4H—SiC as a semiconductor material, a 4H—SiC single-crystal film (hereinafter referred to as “SiC epitaxial film”) is epitaxially grown on a semiconductor substrate made of 4H—SiC (hereinafter referred to as “4H—SiC substrate”) so as to manufacture a SiC single-crystal substrate. ACVD (Chemical Vapor Deposition) method has been used as an epitaxial growth method.
In the epitaxial growth using the CVD method, raw material gas flowing into a reaction vessel (chamber) is thermally decomposed in carrier gas, and silicon (Si) atoms are then deposited continuously on the crystal lattice of a 4H—SiC substrate so as to grow a SiC epitaxial film on the 4H—SiC substrate. Generally, monosilane (SiH4) gas and dimethylmethane (C3H8) gas are used as the raw material gas and hydrogen (H2) gas is used as the carrier gas. In addition, nitrogen (N2) gas or trimethylaluminum (TMA) gas is suitably added as doping gas.
A method for epitaxially growing a SiC epitaxial film on a 4H—SiC substrate has been proposed in which, in the process of epitaxially growing a silicon carbide single-crystal thin-film by a thermochemical deposition method on a silicon carbide single-crystal substrate whose off angle is not larger than 4°, hydrogen chloride gas is introduced at the same time that raw material gas containing carbon and silicon is introduced. The atomic ratio (C/Si ratio) of carbon to silicon contained in the raw material gas is not higher than 1.5 and the atomic ratio (Cl/Si ratio) of chlorine in the hydrogen chloride gas to silicon in the raw material gas is higher than 1.0 and lower than 20.0 (for example, see Japanese Patent No. 4719314).
As another method, there has been proposed a method which is a method for manufacturing a silicon carbide single crystal using a CVD method, in which hydrogenated gas of silicon and hydrocarbon gas are supplied onto a heated SiC substrate together with carrier gas so as to grow the single crystal due to thermal decomposition reaction. In the manufacturing method, a SiC single-crystal substrate inclined at a small inclination angle from a (0001) plane thereof is used as the SiC substrate, and HCl gas is supplied onto the SiC single-crystal substrate simultaneously with the hydrogenated gas of silicon, the hydrocarbon gas and the carrier gas (for example, see JP-A-2006-321696).
However, in prior epitaxial growth methods the growth rate is low to be about several μm/h. To grow an epitaxial film with a thickness (film thickness) of several tens or more μm required for manufacturing a high-voltage device, there arises such a big problem on industrial production that it takes considerable time to grow the SiC epitaxial film. For example, to manufacture a high-voltage SiC semiconductor device with a breakdown voltage of 10 kV or higher, it is necessary to grow a 4H—SiC single-crystal film at least about 100 μm thick on a 4H—SiC substrate. Therefore, the increase of the epitaxial growth rate on industrial production is required.
The present invention is directed to overcoming or at least reducing the effects of one or more of the problems set forth above.